I. Role of protein kinase A (PKA) in mediating smooth muscle relaxation. Using the competitive antagonist of the action of cAMP, R-p-cAMPs, activation of PKA was shown to be primarily responsible for mediating smooth muscle relaxation produced by adrenergic agents and various neuropeptides. II. Gastric smooth muscle cells possess two classes of endothelin receptors, however, only one alters contraction. Gastric smooth muscle cells were shown to possess both ETA and ETB receptors, however in contrast to the pancreatic cells, they were not regulated by agents that activate PLC. Only occupation of the ETA receptor altered contractile behavior. III. Gastric smooth muscle cells possess high affinity galanin receptors which mediate relaxation by activating adenylate cyclase. Galanin was shown to have a direct affect on gastric smooth muscle cells cause relaxation. By binding studies, high affinity galanin receptors were characterized, occupation of which by agonists activated adenylate cyclase. Structure function studies showed the N-terminus of galanin determines receptor affinity and that this affinity is regulated by guanine nucleotide binding proteins. IV. Chimeric galanin analogues are not receptor antagonsists. To investigate whether the two recently described classes of galanin receptor antagonists would be generally useful for investigating its complex effects on gut functions, their ability to alter smooth muscle function was investigated. In collaboration with Drs. Rossowski and Coy (Tulane University), these analogues were found to function as full agonists in both jejunal muscle strips and isolated gastric muscle cells, suggesting they will not be useful to investigate this peptide's role in motility.